Reduction of tolerance effects in the 2nd-order sallen-key filter

In 1967, Saraga provided useful clarification of the factors involved in minimising the effect, on the performance of a 2nd-order Sallen-Key filter (in particular its Q-factor), of variations in its active and passive components. There existed at that time no automatic means of minimising the variation in circuit performance ensuing from component tolerances. For each class of circuit, a theoretical study - such as that of Saraga´s for the Sallen-Key filter - was needed to provide guidelines for the designer. It is now possible to carry out such a minimisation by means of an iterative algorithm. The aim of this paper is to bring such an algorithm to the notice of filter designers, to demonstrate its application to the 2nd-order Sallen-Key filter, and to show how other factors (e.g. less than 100% yield) which are not tractable analytically can easily be taken into account.